The present invention relates to a cylinder head cover for an internal combustion engine.
In recent years, internal combustion engines equipped with hydraulic variable valve actuation mechanisms have been in practical use. Such an internal combustion engine has variable valve actuation mechanisms provided in the vicinity of camshafts. The variable valve actuation mechanisms are actuated by supply and drainage of hydraulic oil to and from the mechanisms. Specifically, such supply and drainage of hydraulic oil are switched through control performed by an oil control valve. The valve timing of intake valves and exhaust valves are thus adjusted. An apparatus that is capable of varying the valve timing of an internal combustion engine as shown above is disclosed in Japanese Patent No. 3525709.
In the configuration disclosed in the above document, a valve case is attached to the top of a cylinder head cover, and an oil control valve is provided in the valve case. Hydraulic oil circulating in a cylinder head is supplied to the oil control valve attached to an upper portion of the cylinder head cover through supply piping formed about the cylinder head. In this configuration, the supply piping is typically formed by coupling metal pipes to one another with union bolts and oil joints.
In such piping, metal pipes need to be supported in a state separated from the surface of the cylinder head cover using supporting members such as union bolts. As a result, the number of components is increased, and the weight of the internal combustion engine is increased, accordingly. This could adversely affect the fuel economy performance. Also, resonance in the metal pipes due to operation of the internal combustion engine could adversely affect the sealing performance of the union bolts and the oil joints.
Recently, to reduce the weight and suppress noise of internal combustion engines, use of resin cylinder head covers have been studied. However, as long as supply piping is formed of metal pipes as discussed above, the problems of an increased number of components and reduced sealing performance are not solved by resin cylinder head covers. This leads to the idea of supply piping integrated with the cylinder head cover of an internal combustion engine.
However, in the case where the supply piping is integrated with the cylinder head cover, as well as in the case where a cylinder head cover is formed of resin, the mere integration of the components does not satisfy the demands. That is, it is desired that such integration increase the strength and reduce the weight of cylinder head covers.